People have preferences and expectations regarding the appearance of certain objects in images. For instance, studies have shown that people prefer the reproduced sky to be more saturated than the real one, and the skin and the grass to be yellower than the real ones.
The colors of skin, sky and foliage are examples of “memory colors.” A memory color refers to the color of a familiar object. An observer chooses to match the color of a familiar object to his or her memory of the color rather than the actual color. Sky, skin and foliage are very familiar objects in an image.
The reproduction of memory colors might be unsatisfactory due to imperfections in digital images and the capture, color processing, and display of digital images. For instance, white balancing by a digital camera might produce memory colors that appear unpleasant.
Even if the memory colors are captured and reproduced accurately, they still might appear unpleasant. For instance, a digital camera accurately captures a grayish-blue sky, and a photo printer accurately reproduces the sky, but the sky still appears unpleasant.
Memory color enhancement is performed on digital images to modify the colors of familiar objects so they appear more familiar and pleasant. These objects are typically identified by image segmentation, and their colors are modified independently of each other. The color of vegetation might be modified to a more pleasant green. Skin color might be modified to appear warmer and more natural. The color of the sky might be modified to a deeper blue.
Although memory color enhancement might produce more pleasant colors for certain objects in the image, it does not necessarily produce a better looking image overall.